This disclosure relates generally to a chemical reactor system for the production of dihydroxy compounds that minimizes pressure drop, channeling, and maldistribution of reactant and product flow through the bed of the reactor system. More particularly, the disclosure relates to the production of 2,2-bis(4-hydroxyphenyl)propane by introduction of a ketone and a phenol compound in an upflow mode from a reactant distribution system, direction of the reactants through a catalyst bed, and removal of products through a product collection system.
Dihydroxy compounds, and in particular bisphenols, are used as raw materials in the preparation of chemical products such as epoxy resins and polycarbonates. They are commonly prepared by the condensation of ketones and phenols. Typical bisphenols include 2,2-bis(4-hydroxyphenyl)propane (also known as bisphenol A, hereinafter BPA), which can be produced by reacting acetone (also known as dimethyl ketone) and a phenol in the presence of an acid.
A packed bed reactor system utilized in the production of bisphenols generally comprises a bed of packed materials such as, for example, catalyst that may be particulate in form (e.g., beaded), to which liquid reactants are introduced. The reactants are made to flow through the bed where they contact each other in the presence of the catalyst and react to form a final product and by products that is removed from a downstream point in the bed. In such packed bed reactor systems. pressure associated with the bed oftentimes has an effect on the physical of the reactor. Differential pressure, which is a measure of the resistance to flow over the height of the packed bed, increases with increased bed height. The differential pressure over the height of the packed bed may compress and deform the catalyst beads causing a reduction in liquid throughput as a result of pressure drop limitations. In response to an increase in the differential pressure, and because the density of the catalyst beads closely approximates the density of the liquid, fluid flow oftentimes suffers significant disruption, thereby resulting in a reduction of the throughput and/or “channeling.”
The BPA reactors oftentimes operate in a down flow mode, where the exothermic condensation of phenol and acetone occurs in the presence of an acidic ion exchange resin (IER) catalyst and optionally in the presence of a co-catalyst promoter. When producing SPA in a downflow mode, the degree of cross-linking of certain IER catalysts directly affects the physical performance of the reactor as well as the reactivity, the selectivity, and the yield of this reactor. Indeed, Increasing the throughput of the BPA reactors operated in downflow configurations involves an increase in pressure drop and an increased risk that the beads will be misshapen and/or that the packed bed will collapse. Hydraulic limitations have also been observed particularly in the case of the IER catalyst having a low degree of cross-linking (e.g., less than or equal to about 2.5%). Although the hydraulic problems are less significant in IER catalysts having higher degrees of cross-linking, the reactivity, selectivity and life time (ton produced per ton of catalyst used) of such resins in the synthesis of BPA also decreases considerably. As such, a more highly cross-linked catalyst is generally more resistant to the hydraulic impact attributable to the particle shape and to the compression mechanism of the particle beads due to pressure. However, higher cross-linked catalyst also tends to be characterized by lower reactivity, lower selectivity, and shortened lifetime.
In an effort to compensate for the hydraulic limitations of catalysts having a lower degree of cross-linking while at the same time retaining the benefits of catalysts having a higher degree of cross-linking, BPA may be produced in a “combi-bed” apparatus, as is disclosed in U.S. Pat. No. 5,395,857 and U.S. patent application Ser. No. 09/258,235. The combi-bed apparatus optimizes the high production rate of BPA indicative of a catalyst having a high degree of cross-linking as well as the increased activity, selectivity, and lifetime of a catalyst having a lower degree (less than or equal to about 2% of cross-linking by combining both catalysts in the same reactor bed. Nevertheless, the capabilities of the combi-bed apparatus remain limited in terms of lifetime and in terms of maximum allowable throughput.
In further attempts to alleviate the problems associated with hydraulic limitations in catalyst beds, reactors have also been constructed to have an increased diameter while maintaining a decreased bed height, thereby allowing the reactors to utilize catalyst having a lower degree of cross-linking while operating with a pressure drop that enables acceptable reactor throughput to be maintained. In still further attempts to alleviate the problems associated with hydraulic limitations, reactants may be fed to BPA reactors in an upflow mode to reduce the effects of pressure drop on the performance of the reactors and to overcome throughput limitations.
Channeling is a condition of flow in which a fluid is permitted to randomly engage some active groups to the exclusion of other active groups. In channeled flow, portions of the bed may be short-circuited and not contacted by the fluid in a uniform and consistent manner. Such a condition can lead to the incomplete treatment or incomplete chemical reaction of the charged reactants. This, in turn, can result in the premature disposal of the catalyst or treatment particles, which translates into loss of part of the value of the catalyst.
Channeling may occur during the operation of a reactor in either the upflow mode or the downflow mode. In the upflow mode, the reactants are pressure-fed at a lower end of the reactor. As the reactants flow to the top of the reactor, they contact each other and the catalyst disposed in the reactor bed and react to form the desired product, which is retrieved from the top of the reactor. If the catalyst is in the form of beads, compression of the beads under their own weight causes a pressure drop to be realized over the height of the reactor. In the downflow mode, the reactants are fed to the top of the reactor. Pressure is typically applied to increase the reactant flow (and therefore the product takeoff rate). In the downflow mode, however, catalyst beads oftentimes compress under the action of the downward flow in addition to compressing under their own weight. Under compression, the catalyst beads may become misshapen and the packed bed may collapse thereby reducing the void fraction of the catalyst bed and magnifying the pressure drop issues.
Because of channeling and the resultant inefficient contact of the reactants with the catalyst, the operation of packed bed reactors is oftentimes significantly hindered, in particular, operations in which significant amounts of channeling occur generally result in low product yield, premature replacement of catalyst beds, and inefficient use of the reactants. This results not only in the cost of new catalyst, but also loss of production during outages, logistical costs of replacement, used catalyst disposal costs, and recovery and recycling of the reactants. Furthermore, a significant financial burden may be realized as a result of costs associated with efforts to improve catalyst technology. Such costs involve the development of alternate reactor geometries but not address the problem of existing reactors that have less favorable geometric features.